1. Field of the Invention
The present invention relates to a filtering technology in a front end module of a wireless communication device.
2. Description of Related Art
In wireless communication devices, reduction in size of a front end module including a duplexer is sought after. In order to achieve the size reduction, some of the components provided in the module are formed inside a substrate. However, it is difficult to form a capacitor or an inductor inside the substrate when it has a large element value.
A front end module as shown in FIG. 1, for example, has been traditionally used. In the front end module shown in FIG. 1, one end of an inductor L101 (2.2 nH, for example) is connected to a terminal 1 of an SAW (Surface Acoustic Wave) duplexer 1001, which is connected to an antenna (ANT), and the other end of the inductor L101 is grounded. One end of an inductor L100 (4.9 nH, for example) is connected to a terminal 2 of the SAW duplexer 1001, which is connected to a transmission circuit, and the other end of the inductor L100 is grounded. Between a terminal 3 and a terminal 4 of the SAW duplexer 1001, which are connected to a receiving circuit, an inductor L102 (8.2 nH, for example) and the primary coil of a transformer T101 are connected in parallel. One end of the secondary coil of the transformer T101 is grounded, and the other end thereof is connected to another circuit. Terminals 5 and 6 of the SAW duplexer 1001 are grounded. The inductors L100 and L101 are matching elements.
FIG. 2 shows frequency characteristics of this front end module. In FIG. 2, the frequency characteristics at the transmitting terminal (TX) and the frequency characteristics at the receiving terminal (RX) are shown. The horizontal axis represents the frequency, and the vertical axis represents the gain. If a wireless communication device is designed to receive through an antenna a signal in the band around 1.5 GHz for GPS (Global Positioning System) and a signal in the band around 2.11 GHz to 2.17 GHz for receiving wireless communication, for example, because the transmission frequency characteristics show excessive gain and the insufficient attenuation amount in the areas indicated with the circles in FIG. 2, a noise that is generated by the transmitting terminal is received by the receiving terminal, resulting in a problem.
Although there exist various conventional technologies with regard to a front end module, a technology that can solve such a problem and that can also achieve the size reduction has not yet been provided.